Because, the chest is not infinite.
it is limited to 65530 slots and with a stack size of 10 you can't even store 1M
if you use a common name, the name should correspond to the truth. if not common then at least you name should be in the mod name.

the name "3.3 mil iron ores or 6.5 mil iron plates or 13 mil steel plates'' wasn't catchy enough. I wish it was infinite too, but the game mechanics and my skills limited me to 65530 slots, sorry.

there is an real infinity chest in the game, you only need to code that you can get only what you put in. THEN the Name would be true.

you mean the chest that provides an infinite amount of items? That's not infinite storage

But it is. store the number of items you put in, then you can manage the items you can put out.
if I think about it correctly, this would even work with a normal chest.

are we talking about the same item?
/c game.player.insert{name="infinity-chest", count=1}
That chest has 48 slots.

yes, but you don't need to fill all slots. only count the item, which a user puts in, then remove the items.
let only 1 slot for each item type filled. this works with any chest, so you can store 48 different item types infinite.
if you want to use only 1 item type, the infinity-chest can remove all items automatically.

The same without a mod, needs more place:
https://prnt.sc/10s9bik